The present invention relates to a method for favouring, by causing a depression, the production of effluents of a producing zone crossed by at least one deflected well or drain, such as a petroliferous zone. What is called a deflected well is any well at least part of which is substantially horizontal or little inclined in relation to the horizontal.
One of the interests of deflected wells is to allow a better scavenging of the oil effluents contained in the formations crossed and thereby to improve recovery.
Optimum recovery, for a given scavenging mechanism, is obtained when the scavenging front moves parallel to the deflected drain. The regularity of the scavenging front is sometimes difficult to keep because of heterogeneities of the reservoir such as fractures or channels, etc, changes in the drain geometry or disturbances linked to the flows in the drain such as pressure drops.
A well-known method for scavenging a producing zone consists in taking down therein a pumping device to suck out the effluents when the pressure in the formation becomes insufficient. The deflected well crossing the producing zone is equipped with a casing that is perforated in the part thereof which crosses the producing zone. A tubing is taken down into the zone to be activated. If necessary, a pump is intercalated on the tubing in order to produce a depression. An example of a pumping device is for example described in French patent application EN. 90/08,270. The depression caused by such a tubing is maximal in proximity to the lower end thereof and, because of the pressure drops, it decreases rapidly with the distance, so that the suction pressure quickly becomes insufficient to obtain a correct scavenging of the producing zone.
It is often difficult, in practice, to increase the depression at the lower outlet of the tubing in order to obtain a sufficient depression at all the points of the zone to be activated, either for reasons linked with the pumping assembly proper or because of the structure of the activated zone. As a matter of fact, in some basins, the layer containing the oil is relatively thin. It is bordered on one side with a gas accumulation or an aquifer. It may also lie between a gas accumulation and an aquifer. In this case, too strong a depression at the outlet of the tubing has the effect of also bringing in the gas or the water from the adjacent layers.